1. Field of this Invention
This disclosure relates to a semiconductor integrated circuit device, and more particularly, to a semiconductor integrated circuit device including circuits for programmable bus termination and impedance driving.
2. Description of Related Art
In designing high frequency integrated circuit devices associated with a double data rate (DDR) memory, it is becoming important with input/output AC characteristics of data, address, and control signals in accordance with the advancement of functionality in semiconductor device industries. The AC characteristics are more affected from the property of channels linking two or more numbers of devices, rather than from integrated circuit devices or controllers for managing the devices. Thus, it is essential to regard the channel characteristics in designing the high frequency integrated circuit devices.
There have been various studies to improve the channel characteristics, such as techniques using programmable circuits for on-die termination and off-chip driving. Several disclosures about the circuits of on-die termination and off-chip driving are proposed in U.S. Pat. No. 5,666,078 entitled “Programmable impedance output driver”, U.S. Pat. No. 5,995,894 entitled “method for controlling the impedance of a driver circuit”, U.S. Pat. No. 6,157,206, and Korean Patent No. 10-0332455.
As well known persons skilled in this art, the impedances of the on-die termination circuit and the off-chip driver are adjusted different from each other. For instance, an impedance of the on-die termination circuit is established to 60Ω while that of the off-chip driver is set to 40Ω. The preceding arts usually employ additional control circuits and external reference resistors to control the impedance of the on-die termination and off-chip driving circuits.
However, those techniques enlarge chip sizes and the number of pins to increase the burden of designing semiconductor integrated circuit devices.